Tailpipe thrust augmentor



W. R. TRAVERS v TAILPIPE' THRUST AUGMENTOR Filed March 30, 1955 wml# Ricks? L.

United States PatentN 2,913,874 Y 'rAxLPrPE "munis1.-AUGMnlsrron William Raphael Travers, Madeira, Ohio, `assigner to General Electric Company, a corp'oration'of New York This invention relates fuel burners and, more particularly,` toa device for burning fuel `in the vexhaust duct or tailpipe of a jet engine.

Under certain operating conditions, itA is desirable tov augment the thrust output of a jet engine.' Numerous methods of augmentation have beenV known" and u'sed in the prior art. One method of augmentation is by injecting and burning additional fuel in the exhaust 'duct or tailpipe of the jet engine downstream of the turbine wheel. Burning has been accomplished in the prior art by providing a pilot or primary burner in the tailpipe in combination with second fuel'injection means so that combustion is initiated in -the pilot or primary burner and is `causedfto spread to the fuel injected by the second fuel injection means. Burning is thereafter` continuously maintained by injecting additional fuel. Y v

. The velocity of the combustion products and excess air in the tailpipe is often greater `than the velocity offlame propagation. -The use of a pilot burnerprovides one method of reducing` the flow velocity in a 'portion of thetailpipe sufficiently to permit the burning of fuel `to be initiated. n .y

Pilot burners, as heretofore known, reduce, the velocity of flow by creating a turbulent condition within the `pilot burnerwhich leads to non-uniform mixtureof the air and fuel resulting in inefllcient combustion both infthe4 pilotburner `and .the air fuel mixture near the second fuel injection means. A further disadvantage vof tailpipe burners-as heretofore known is that the amount of fuel burned to obtain a given amount ofl thrust increase requires the use of an extra fuel pump to fully supply` the needs of the tailpipe burner. AThe high fuel rates are due to the inefficiency in the burning of fuelV caused by the turbulence created by the pilot burner.' The use of lan extra fuel pump is, of course, disadvantageous ,in `aircraft installations where a primary objective is to climi# nate as much excess weight as possible. The added fuel pump adds substantially to the weight` of the'A engine. It is a general object of this invention to obviate `the aforementioned difficulties.

Another object of this invention is the provision of a tailpipe thrust augmentorwhereby the pilot burner is supplied with air in such a'rnanner that a vortex substantially coaxial' with the axis of thetilpipe is formed thereby obtaining a more uniform airfue1 mixture resulting in elcient combustion in the 'pilotburner and'at the second fuel injection means. j,

Itis a further object of this invention to provide a tailpipe thrustaugmentor which does not require the use of an extra fuel pumpfor injecting fuel due to the improved combustion efl'iciency which reduces the required fuel flow'for a given amount of thrust' augmentation'.`

Briefly stated, in accordance with one aspect of my invention, I provide a tailpipe thrust augmentor including a pilot burner and second fuel injection means having means cooperating with the pilot burner for causing a vortex in the pilot burner of the burning air-fuel mixture substantially coaxial with the tailpipe so as to improve 2,913,874 Patented Nov. 24, 1959 ICC 2 the burning `characteristics within the tailpipe. Fuel is supplied to the pilot burner and second fuel injection means from a regulator or control valve which meters fuelin proportion to the compressor discharge pressure of the jet engine.

The invention will be better understood from the following description taken in connection with the accompanying drawing wherein, Figure 1 is a longitudinal view, partially ,insectiom of a tailpipe augmentationsystem of a jet engine mountedin an aircraft; uFigure 2 is an enlargedl fragmentarycross-sectional view of the pilot or primary burner; and Figure 3 is an end view, partial in section, taken along the lines 3 3 of Figure 1.

Figure ljshows the tailpipe augmentation system as itfmay-be mounted in` anaircraft. The rear portion of a' jet` engine which may be, of the type having a compressor, combustion chamber and turbine in series flow relation is generally `indicated at 1. The engine including the rear portion `1 may be mounted in an aircraft as generally indicated at 2. The rear portion of the jet engine 1 comprises a turbine casing 3 and an outer exhaust cone 4 held together at their respective radial flanges 5 and 6 by meansof, suitable clamping members, as for example, the bolts 7. l The outer exhaust cone 4 is connected toa tailpipeV 8 at their respective radial flanges 9 and 10 byV anysuitable `clamping means (not shown). Thetailpipe 8 is further connected to the extension 11 at the flanges 12 and 13v which may be similarly secured by suitable'clampngimeans (not shown). A variable nozzle, generally indicated at 14, is mounted at the end of the duct formed by the-outer exhaust cone 4, tailpipe 8, and extension 11, and may be of any form well known in the jet engine art as shown for example in U.S. Patent 2,630,673, Woll, assigned vto theassignee of the present application. i Y

fMounted within the outer exhaust cone 4 and substantially coaxial therewith istheinner cone 15-which may take the form of a Vfrustrum of a cone. vThe annular space 16 defined by the youter exhaust cone 4 and ;the innerv cone"`15 serves as .an exhaust, passagewayforfthe fluid consisting of combustion gases and excess ainxdischarged by the turbine (not shown) mounted within` the turbine casing 3. A primary or pilot burner, as indicated generally at 17 and shown in detail in Figures 2 and 3, is mounted at the end of `the inner cone 15 and Iis substantially coaxial. with theouter exhaust cone 4 and the tailpipe 8. y Y

` The primary or pilot burner 17 comprises a hollowed out or sheltered zone 18 mounted at the end of and within the inner cone 15 and connected thereto by meansof the annularportion 19. Although the hollowed out or sheltered zone `18 is lshown by way of example as ybeing hemispherical in shape, it is to be understoodthat other shapes will be satisfactory in practicing the present invention. Extending axially with respect to the centerof the inner c one V15vfrom the annular portion 19 are a plurality of vanes or blades 20 each mounted at substantially the same!` distance from the extended vaxis of the innercone 15 and having substantially the sameangle of attack with respect thereto. An annular ring-like membe1j`2 1 is attached to the end 22 of `each of the varies` or` blades 20 in order to maintain rigidityofthe vanes` 20 when the burner is `in operation. An annular deflector or scoop 23 is mountednear theends 22 ofthe vanes 20 and may be secured for. convenience to theperiphery;

of thering-like: member 21.

I also provide fuel supply, injection and ignition means. As illustrated, these means comprise a fuel control reg# ulator 24, the operation of which will be hereinafter described, which is supplied with fuel from the main fuel pump by means of the conduit 25. A conduit 26 supplies air from the jet engine compressor or other pressure sensing point in the engine to the fuel control regulator 24 for control purposes. Fuel is supplied from the control 24 by means of the conduit 27, T 28, branch conduits 29 and 30, the T pieces 31 and 32, and the connecting conduits 33 and 34- of the fuel' spray nozzles 35 mounted in the hollowed or sheltered zone l1.8 of the primary or. pilot burner 17 and the fuel spray ring 36.

The fuel spray ring 36 is shown as being circular in shape, but may take other forms which would serve the same purpose. The spray ring 36 is mounted in a plane which is substantially normal to the axis of the inner cone and is approximately coincident with the trailing edge of the primary or pilot burner 17. The fuel spray ring 36 may also vary in position from that shown to obtain eicient burning and under some circumstances it may be desirable to mount it somewhat downstream of the trailing edge of the pilot burner 17. The fuel spray ring 36 communicates with the connecting conduits 34 by means of the conduit extensions 37 and the radial conduit arms 38. The radial conduit arms 38 are rigidly attached to the pilot burner by means of the brackets 39 attached to the ring-like member 21. The radial conduit arms 38 and the brackets 39 may be several in number in order to properly support the fuel spray ring 36. It is to be noted that the conduit extensions 37 connecting the conduits 34 to the radial conduit arms 38 lies between a pair of adjacent vanes 20. A suitable igniter 40, if needed, may be mounted at any suitable location in the h ollowed portion 18 of the primary or pilot burner 17. The fuel spray ring 36 is provided with a plurality of apertures 41 about its outer periphery in order to inject fuel into the uid stream. Although the apertures 41 are shown as spraying fuel radially with respect to the center of the duct, it is to be understood that other spraying directions may be used where desirable.

In operation, the iluid consisting of combustion products and excess air exhausted from the turbine casing 3 passes rearwardly in the exhaust passageway through the annular space 16. A portion of the uid is directed radially inward through the vanes by the deector or scoop member 23. The angle of attack of the vanes 20 is such that it causes the formation of a vortex generally indicated at 42 centrally of the pilot burner 17, the axis of which is substantially coaxial with the axis of the tailpipe 8.

During periods when it is desired to augment the thrust output of the engine, fuel is injected through the nozzles 35 into the pilot burner 17. The fuel is intermingled with the excess air of the vortex formed within the pilot burner 17 and forms a very well mixed and uniform air-fuel mixture which may be ignited by the igniter 40 when separate igniter means are found necessary. The burning vortex as generally indicated at 42 within the pilot burner 17 will ow helically out of the open end of the burner 17. A rnajor portion of the fuel is injected into the tailpipe 8 through the apertures 41 of the fuel spray ring 36. Due to the velocity of the exhaust fluid, the spray emitting from the apertures 41 is immediately caused to form a combustible mixture which flows rearwardly in the tailpipe 8. The combustible mixture formed from the fuel sprayed through the apertures 41 is ignited from the burning llame or vortex 42 owing out of the pilot burner 17. Upon ignition of the fuel injected through the apertures 41, a continuously burning flame occurs in the tailpipe 8 until such time as the fuel'ow is completely shut off.

Due to the arrangement of the fueljspray ring 36 and the apertures 41 therein, the uid flowing through the annular space 16 causes the fuel-air mixture to concenlthe burning in the tailpipe occurs in a core, the outer boundaries of which are indicated by the numbers 43. It will of course be apparent that the advantages of burning the fuel within a core as dened by the boundaries 43 is that the tailpipe S is not subjected to the extremely high temperatures of the burning fuel.

As has been previously stated, one of the features of this invention is the elimination of a separate fuel pump for 'supplying fuel to the augmentation system. Due to the efficient burning within the tailpipe 8 resulting from the formation of the vortex 42, it is possible to eliminate the need of an extra fuel pump and, in its place, use a very simple fuel control 2'4. The fuel control 24 is of any well known direct ratio type of metering device, such as a bellows .type control, which meters fuel flow in direct proportion to and responsive to the discharge air pressure of the air compressor or other pressure occurring within the engine. Although the structural details of such a metering device are not shown, it will be obvious to those skilled in the art that any type of direct -ratio pressure responsive metering device will accomplish this result. A control of this type will at all times assure a proper air-fuel mixture since the amount of fuel i11- jected will be in direct proportion to the amount of excess air flowing through the jet engine.

While a particular embodiment of the invention has been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claim all such changes and modifications that come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A jet engine having, in combination', an exhaust passageway, combustion products and air owing in said exhaust passageway, a pilot burner including fuel injection and ignition means mounted centrally of said passageway, said pilot burner having a plurality of longitudinally extending peripheral guide vanes, an annular deflector cooperating with said guide vanes to direct a portion of the ow in said passageway through said guide vanes into said burner, the angle of attack of said guide vanes causing the formation of a vortex within the pilot burner, said vortex being substantially coaxial with the exhaust passageway and extending longitudinally thereof, a fuel spray ring mounted within said passageway substantially surrounding the vortex and beyond the vane containing portion of the pilot burner, said fuel spray ring having apertures for spraying fuel into said passageway, means including a regulator having a single fuel control valve for metering fuel to the pilot burner and the fuel spray ring wherein the control valve meters fuel in proportion and responsive to the fluid pressure at a point in the jet engine, the fuel injected from the spray ring being ignited by the pilot burner.

References Cited in thele of this patent UNITED STATES PATENTS 2,674,846 Bloomer et al. Apr. 13, 1954 2,687,010 Ellis Aug. 24, 1954 2,704,435 Allen Mar. 22, 1955 2,714,803 Abild Aug. 9,1955

2,807,316 Jackson Sept. 24, 1957 FOREIGN PATENTS 706,698 Great Britain Apr. 7, 1954 

